Carbon can be deposited in various crystal structures. For example, in the form of a diamond structure, as a monolayer, multilayer structure (multilayer sheets) such as graphene, as tubes such as “carbon nanotubes”, or as fullerene or as fibers. CVD devices are used to deposit such carbon structures, in particular nanostructures, which have structure sizes in at least one dimension from a fraction of a nanometer up to several hundred nanometers. In this case, together with a carrier gas, for example, argon or hydrogen, a carbonaceous starting material, for example, methane or acetylene, is introduced into the process chamber of the CVD reactor. Activating or dissociating the introduced carbonaceous starting materials thermally or by means of a plasma is known. For example, U.S. Pat. No. 8,398,927 B2 describes a plasma-enhanced CVD (PE-CVD) and US 2006/0185595 A1 describes a hot filament CVD (HF-CVD). In the case of the PE-CVD, a plasma is ignited inside a gas inlet element. For this purpose, the device has a plasma electrode to which electrical voltage is applied. In this way, radicals are generated, which can enter through the gas outlet opening of the gas inlet element into a process chamber, where they are deposited on a substrate arranged on a heating element with formation of the nanostructures. In the case of the HF-CVD, the carbonaceous starting material is heated using a hot filament inside or also outside a gas inlet element. In the case of the HF-CVD, a plasma, using which radicals are generated, can be ignited directly above the substrate. The ignition of a plasma directly above the substrate is disadvantageous, however, since high-energy ions form in the plasma, which have an etching effect on the substrate.
Devices for depositing carbonaceous structures using a plasma are also known from U.S. Pat. No. 6,499,425 or U.S. Pat. No. 6,161,499.